Many various caulking guns and the like dispensing devices are known, which are adapted to be used in connection with interchangeable cartridges available in standard sizes. Such caulking guns are also known whereby the material is expelled from the cartridges by means of compressed air introduced into the cartridge from behind. When it is a question of detachable cartridges, the replacement is often complicated and time-consuming. Often they must be situated in a closed container being screwed off and on the remaining portion of the dispensing device during the replacement of the cartridge. The known caulking guns sometimes require that the front end of the cartridge must be pressed hard against a packing, and when the sealing of this packing is insufficient there is a risk of compressed air leaking round the cartridge, past this packing, and into the expelled material.
European patent application No. 52,060 discloses a dispensing device comprising a holder receiving a cartridge and a sealing piston. This sealing piston is adapted to be pressed against the rim of the cartridge so as thereby to close said rim when the cartridge is being pressed against the front end of the holder. The sealing piston is constantly biased by a spring in a direction towards the front end of the holder, and furthermore it is displaceably mounted in axial direction partly inside a cylinder and partly on a bolt coaxially secured in said cylinder. The head of the bolt is used for restricting the movement of the piston forward towards the front end of the holder, and when the piston abuts this head the passage is closed for the compressed air from the interior of the cylinder to the space surrounding the bolt and the clearance usually present between the bolt and the piston. In addition, bores are present to ensure that the pressure within the cylinder is not so high when the dispensing device is not in use and no cartridge is situated in the dispensing device that the circumferential lip of the piston is bent forward out of engagement with the cylinder, said lip sealingly abutting the inner side of the cylinder.